Vehicle Systems and Malfunctions
This domain tests recognition of brake, air, cooling, electrical, and tire problems, and the correct immediate response. The exam emphasizes warning thresholds and safe shutdown decisions.
Air brakes and ABS
Monitor the air gauge. The low-pressure warning must activate before 60 psi, and spring brakes apply between 20 and 45 psi. If pressure falls, stop safely before the spring brakes apply. ABS is an add-on; it prevents wheel lockup and helps steering, but it may not shorten stopping distance. Do not pump ABS brakes-apply firm, steady pressure and steer.
Other systems
Watch coolant temperature, oil pressure, and the voltmeter. A rising temperature may mean a coolant leak or fan problem; stop and investigate before overheating. A tire failure calls for holding the wheel and slowing gradually. Brake fade means the brakes are overheating; slow down, downshift, and use engine braking.
Worked example
You hear the low-air warning at 58 psi. The warning is working as designed because it sounds before 60 psi. Continue to monitor; if pressure keeps falling toward 45 psi, the spring brakes will begin to apply. Move to a safe stop before that happens. Do not fan the brakes to build pressure-find the leak or call for service.
Traps that cost marks
Ignoring a low-air warning because the vehicle still stops; fanning brakes to raise pressure; pumping ABS; and continuing to drive with rising coolant temperature. Also do not assume an ABS warning light means normal brakes are gone-but do get the system checked.